There is a need in the industry for improved polyolefins, including particularly polyethylene. Polyethylene is useful for the manufacture of a variety of articles, including molded articles, films, and other structures. Improved polymeric articles may provide certain desired optical properties such as reduced haze or increased clarity. Such articles are made by applying nucleating or clarifying agents and perhaps other additives in the polymer prior to manufacture of articles using the improved polymer. Improved mechanical properties of such polymers also are desirable.
Polymer compositions may be rendered molten for manufacture into a wide variety of articles. Such articles may include films, fibers, and various types of molded articles. Various polymer processing techniques are known, including extrusion, blowing, molding, compression, and injection, in which the molten polymer is cooled and shaped into a solid mass. Each process has its own particular physical and chemical effects upon the polymer. Further, each process is customized to achieve exactly the performance required from the polymer, using the least amount of energy, and at the maximum rate of production. In general, the use of one compound or formula in one type of polymer processing technique does not predict success using the same formula in another type of processing technique. Extensive trial and experimentation is needed to determine that a particular formulation is or is not suitable for a particular type of polymer process.
Thermoplastic compositions must exhibit certain physical characteristics to facilitate widespread use. Specifically within polyolefins, for example, uniformity in arrangement of crystals upon crystallization is sometimes necessary to provide an effective, durable, and versatile polyolefin article. To achieve desirable physical properties, certain compounds and compositions can be employed to provide nucleation sites for polyolefin crystal growth during molding or fabrication. Nucleating agents are known to modify the crystalline structure of thermoplastic polymers.
The use of nucleating agents may increase the temperature and the rate of crystallization. Compositions containing such nucleating compounds crystallize at a much faster rate than non-nucleated polyolefins. Crystallization at higher temperatures results in reduced fabrication cycle times and a variety of improvements in physical properties such as stiffness.
Nucleating agents provide nucleation sites for crystal growth during cooling of a thermoplastic molten formulation. The presence of such nucleation sites results in a larger number of smaller crystals. As a result of the smaller crystals formed therein, clarification of the target thermoplastic may be achieved. However, excellent clarity is not always a result. The more uniform (and smaller) the crystal size, the less light is scattered. Thus, the clarity of the thermoplastic article itself may be improved. Thus, thermoplastic nucleator compounds are important to the industry, as they may provide enhanced clarity, improved physical properties, and faster processing.
Extrusion of polymer is a common manner of making extruded plastic articles. Other processes, however, are known for processing polymers. Processing techniques, temperatures, and the like vary greatly among various types of polymer processing techniques. In general, it is not predictable or certain that any particular formulation used in one type of processing (such as extrusion) could apply or work in a different type of polymer processing technique, using different temperatures, mechanical processing methods, cure times and the like. Further, each type of polymer and each nucleating agent itself provides unique properties. It is not predictable that an additive or procedure used with one type of polymer would perform satisfactorily with another polymer.